Ministry of Science & Technology
New artificial light-harvesting system using organic nanotubes useful for solar cells, photocatalysis, optical sensors & tunable multi-color light emitting materials
Inspired by natural photosynthetic systems, researchers have developed a new method of harvesting artificial light using organic nanotubes, which can be utilized in solar cells, photocatalysis, optical sensors, and tunable multi-color light-emitting materials.
In nature, plants and photosynthetic bacteria capture sunlight and deliver it to the reaction center through a cascade of energy and electron transfer steps for its eventual storage in the form of chemical energy. The antenna chromophores in the light-harvesting complexes are precisely aligned into arrays by the surrounding proteins, which in turn allows the energy migration between them in a highly efficient manner. Mimicking natural photosynthetic systems and understanding the fundamental processes of energy transfer has gained enormous interest in recent years, especially for systems that need energy conversion and storage.
Towards this direction, Dr. Supratim Banerjee from the Indian Institute of Science Education and Research  Kolkata, an autonomous Institute under the Ministry of Education, and Dr. Suman Chakrabarty from the S. N. Bose National Center for Basic Sciences , Kolkata, an autonomous institute of Department of Science and Technology  carried out experimental and computational investigations on artificial light-harvesting in organic nanotubes derived from the union of an organic fluorescent molecule and a therapeutically important biopolymer. The former is an amphiphilic cationic molecule called cyano stilbenes , and the latter is an anionic therapeutically important bio-polymer called heparin  in aqueous media.
In the presence of heparin, the cationic cyano stilbenes employed in this study formed nanotubes with bright greenish-yellow emission through an electrostatically driven co-assembly process. Just like the antenna chromophores or pigmented  membrane-associated vesicles used to perform photosynthesis in bacteria, the nanotubes acted as highly efficient energy donors  in a system that mimicked the natural photosynthetic process.
They donated energy to acceptor dyes such as Nile Red and Nile Blue, resulting in emission color tuning from initial greenish-yellow to orange-red, including white light. The energy transfer phenomenon demonstrated in this study is known as FRET , which has significant importance in different applications such as the determination of DNA/RNA structures, mapping biological membranes, real-time PCR tests, and so on. The future is moving towards the conversion of solar energy for storage as chemical or electrical energy, and the process of energy transfer is a key factor for such applications.
In the study published in Chemical Science, the flagship journal of the Royal Society of Chemistry, the formation of the nanotubes was investigated by employing absorption and fluorescence spectroscopy, transmission electron microscopy , and fluorescence lifetime imaging microscopy  studies. Molecular Dynamics  simulation studies demonstrated that the cyano stilbene molecules formed cylindrical structures in the presence of heparin. The local molecular level interactions and packing of the cyano stilbene chromophores that led to the formation of one-dimensional nanostructures were also visualized and quantified through the simulation studies. Due to the temperature responsiveness of the FRET process in these systems, they were further employed as ratiometric emission thermometers  in the temperature range 20–90 °C, and this highlighted a practical application of these artificial light-harvesting systems.
Publication link: https://dx.doi.org/10.1039/d3sc00375b
For more details, please contact:
Dr. Supratim Banerjee  and
Dr. Suman Chakrabarty .
<><><><><>
SNC/PK
(